FIELD OF THE INVENTION
This invention relates to imaging elements and more particularly to photographic imaging elements.
Support materials for imaging elements often employ layers comprising glassy, hydrophobic polymers such as polyacrylates, polymethacrylates, polystyrenes, or cellulose esters, for example. One typical application is as a backing layer to provide resistance to scratches, abrasion, blocking, and ferrotyping. The latter two properties relate to the propensity of layers applied onto the support material or imaging element to stick together as a result of the adverse humidity, temperature, and pressure conditions that may occur during the manufacture and use of the imaging element.
These glassy polymers are typically coated from organic solvent-based solutions to yield a continuous film upon evaporation of the solvent. However, because of environmental considerations, it is desirable to replace organic solvent-based coating formulations with water-based coating formulations. The challenge has been to provide imaging elements containing layers having similar physical and chemical properties in the dried film to that obtained with organic solvent-based coatings, but which are the result of water-based coating compositions substantially free of organic solvents.
Water insoluble polymer particles contained in aqueous latexes and dispersions reported to be useful for coatings on photographic films typically have low glass transition temperatures (Tg) to insure coalescence of the polymer particles into a strong, continuous film. Generally the Tg of such polymers is less than 50.degree. C., frequently the Tg is no more than 30.degree. C. Typically these polymers are used in priming or "subbing" layers which are applied onto the film support to act as adhesion promoting layers for photographic emulsion layers. Such low Tg polymers, although useful when they underly an emulsion layer, are not suitable as, for example, backing layers since their blocking and ferrotyping resistance are poor. To fully coalesce a polymer latex with a higher Tg requires significant concentrations of coalescing aids. This is undesirable for several reasons. Volatilization of the coalescing aid as the coating dries is not desirable from an environmental standpoint. In addition, subsequent recondensation of the coalescing aid in the cooler areas of the coating machine may cause coating imperfections and conveyance problems. Coalescing aid which remains permanently in the dried coating will plasticize the polymer and adversely affect its resistance to blocking, ferrotyping, and abrasion. Thus, there is a need for imaging elements containing layers that perform various functions not having the disadvantages associated with layers applied from organic solutions.